Antennas

The lightning protection is doable. Since the field is coupled magnetically, it can be placed in the vicinity of a lightning absorbing spike.

The omni directional sensitivity is more of a problem. Physics dictates how the waves propagate

Rene

Given that AM band transmitters are all earth bound.

Martian spacecraft notwithstanding, of course.

..... Phil

Have some words gone missing?

Otherwise, I don't see the connection between a 'ferrite loopstick antenna', which is typically 100 to 200 mm long, 'serious lightning protection' and 'a

Is this about a transmitting antenna?

Chris

When I used to run into such "unreasonable" specs, I would initially quote exactly what they were asking for. In this case, it's possible to deliver your abreviated list of specs. Although it's rather unusual, simply mount the loopstick ferrite rod antenna vertically, and you'll have an omnidirectional pattern. However, it's not a hemispherical pattern, as there will be no pickup in line with the rod. More commonly, the loopstick is horizontal, and the user is expected to orient the radio in the optimum direction.

"Serious" lightning protection is possible. However, your customer may not like the cost. Send the specs to a company that deals in such protection (i.e. Polyphaser) and see what they have to offer. If the specs are inflated, the recommended protection will be equally inflated. The big problem is not designing such a lightning protection system. It's testing it and demonstrating that it meets the specs. Be careful here.

... and then it would be oriented for horizontal polarisation, but broadcast radio in the medium-wave band is usually transmitted using vertical polarisation (for several good reasons), so it might not perform well.

Chris

In such a case you may have to carefully ease them back to the basics but without explicitly saying that. Maybe something along these lines:

True. Next time you try an AM radio with a loopstick, rotate it around to see how sensitive is is to polarization. You'll probably get a nice null along the loopstick axis, orientation doesn't seem to make much difference.

Also, if you don't mind using 3 loopsticks, it can be made polarization insensitive.

Combined Multi-Polarization Loopstick and Whip Antenna.

Medium-wave polarisation indoors is rarely pure because of metalwork like pipes and wiring that usually surrounds the receiver - it cleans up outdoors in open spaces. A vertical whip connected to a high-input-impedance amplifier would provide an omni pattern in the horizontal plane, but the amplifier would have to provide low intermodulation and could be difficult to design.

We could do with hearing from the OP whether the intention is a receiving antenna or a transmitting antenna, bearing in mind the stuff about lightning protection!

Chris

Yes, loop antennas intrinsically have a lemniscate pattern (figure-8, two diametrical lobes and two deep notches). I had to dig up the word cause i could not remember it.

No words missing, it is a receive antenna for US AM Radio. 530-1710 kHz.

Alas, i do not have newsgroup access at work. But i got back to this just as fast as i could find it. Oh, and thanks to all already.

I would really like it if they could become interested enough to learn it, it would really make my day.

So where does the 'serious lightning protection' come in? Do you really mean lightning protection (see

Chris

Depends on who they are. For example, if it's folks with a vested and serious financial interest in the business I usually begin to explain the cost implications of such a spec. Kind of a cost benefit analysis.

I truly hope it's not a bureaucrat you have to deal with because then this could be next to impossible.